Gas separation by pressure swing adsorption is achieved by coordinated pressure cycling and flow reversals over an adsorbent bed which preferentially adsorbs a more readily adsorbed component relative to a less readily adsorbed component of the mixture. The total pressure is elevated during intervals of flow in a first direction through the adsorbent bed, and is reduced during intervals of flow in the reverse direction. As the cycle is repeated, the less readily adsorbed component is concentrated in the first direction, while the more readily adsorbed component is concentrated in the reverse direction.
The conventional process for gas separation by pressure swing adsorption uses two or more adsorbent beds in parallel, with directional valving at each end of each adsorbent bed to connect the beds in alternating sequence to pressure sources and sinks, thus establishing the changes of working pressure and flow direction. This conventional pressure swing adsorption process also makes inefficient use of applied energy, because of irreversible expansion over the valves while switching the adsorbent beds between higher and lower pressures.
The prior art also includes the following pressure swing adsorption devices with cyclically operated volume displacement means reciprocating at the same frequency at both ends of an adsorbent bed, to generate pressure changes internally and thus improve energy efficiency.
Keller (U.S. Pat. No. 4,354,859) has disclosed a single bed pressure swing adsorption device for purifying both components of a binary gas mixture fed to a central point of the adsorbent bed. This device has volume displacement means which may be pistons or diaphragms, of specified unequal displacement at opposite ends of the bed.
My U.S. Pat. No. 4,702,903 discloses use of modified Stirling cycle machines for performing gas separations, in which a temperature gradient is imposed on the adsorbent bed which also serves as a thermal regenerator, so that heat may be applied directly through the modified Stirling cycle as an energy source to perform pressure swing adsorption gas separations.
My U.S. Pat. Nos. 4,801,308 and 4,968,329 disclose valve logic means to provide large exchanges of fresh feed gas for depleted feed gas. Such large feed exchanges, or effective scavenging, may be required when concentrating one component as a desired product without excessively concentrating or accumulating other components, as in concentrating oxygen from feed air containing water vapour whose excessive concentration and accumulation would deactivate the adsorbent.
My U.S. Pat. No. 4,816,121, which is concerned with separation of chemically reactive gases and vapours, describes an embodiment in which a product or the reaction is condensed as a liquid within the apparatus, and this liquid fills a U tube interconnecting two identical gas phase working spaces. A hydraulic energy conversion means, such as a reversible pump-turbine, controls oscillating flow of liquid in the U tube, associated with cyclic volume changes and pressure changes in the two working spaces, in opposite phase.